Chapter 22 : Gene Transfer in Plants by Agrobacterium tumefaciens

Abstract:

In this student activity, students inoculate plants with the bacterium Agrobacterium tumefaciens and observe the subsequent plant tumor formation. The common soil bacterium Agrobacterium tumefaciens causes crown gall disease in many dicotyledonous plants. Virulent strains of A. tumefaciens contain genes that cause the plant cells to divide. The plasmid used by A. tumefaciens is the tumor-inducing, or Ti, plasmid. Chemicals secreted from freshly wounded plant tissue attract A. tumefaciens to the wound site. The injected bacterial DNA diverts the plant cell's machinery to tasks that support the growth and reproduction of A. tumefaciens. The strain-specific opine also promotes the conjugational transfer of tumor-inducing plasmids from that virulent strain to avirulent (plasmid-free) strains of Agrobacterium. The gall induced by A. tumefaciens is located at soil level where the roots join the stem (the crown). The vir genes that control gene transfer ability remain intact. Once individual plant cells have received new genetic information, the problem becomes how to regenerate whole plants from these cells. A. tumefaciens is an effective vector for tobacco, petunias, tomatoes, and other dicots—plants with two seed leaves. Microinjection is a new twist on an old idea. Biologists first used fine glass microtools in the late 1800s to dissect animal tissues. Using electroporation, scientists shock protoplasts with electricity until they become receptive to foreign DNA.